Ballast transformer for electric discharge devices



i 21, 1957 I c. E. STRECKER 2,793;326

BALLAST TRANSFORMER FOR ELECTRIC DISCHARGE DEVICES Filed Dec. 9, 1954 2Sheets-Sheet 1 //7 1/922 tor Char/6S 5 Strife/f9;

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1957 c. E. STRECKER 2,793,326

BALLAST TRANSFORMER FOR ELECTRIC DISCHARGE DEVICES Filed Dec. 9, 1954. 2Sheets-Sheet 2 /z71 ez72for: Char/es 5 Sit/"eater".

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United States Patent BALLAST TRANSFORMER FOR ELECTRIC DISCHARGE DEVICESCharles E. Strecker, Danville, Ill., assignor to General Electricompany, a corporation of New York Application December 9, 1954, SerialNo. 474,100

4 Claims. (Cl. 315-257) This invention relates to electric dischargedevices, and more particularly to ballast transformers for use instarting and operating circuits for such devices.

It is a characteristic of electric discharge devices, such asfluorescent lamps, that their internal resistance decreases as thecurrent flow therethrough increases. It is, therefore, necessary in theinstallation of such devices to provide means which will limit thecurrent flow through the device to a safe value. In addition, it mayalso be desirable to provide a higher voltage for initially starting orcausing a discharge in the device than is conveniently available. Whenelectric discharge devices are operated on alternating current, it isconventional practice to'provide a single high reactance ballasttransformer to perform two functions, i. e., limit the current and provide a high initial starting voltage. Such a transformer provides a highopen circuit voltage for starting and also, by virtue of its highreactance, provides impedance during normal operation to limit thecurrent flow.

A high reactance transformer is one in which the primary and secondarycoils are loosely coupled, so that when the transformer is carrying loadthere is a substantial amount of leakage flux, and the voltages inducedin the coils by this leakage flux cause the transformer to have arelatively high effective series reactance, commonly known as leakagereactance. The conventional way of constructing such a transformer is toarrange the primary and secondary coils on difierent parts of themagnetic core and to provide a magnetic shunt between the coils therebyproviding a path for the leakage flux. This shunt is usually providedwith an air gap so calibrated that the operating current of thesecondary coil of the transformer will be limited to a desired value.The high starting voltage is frequently achieved by using a transformerwith the coils connected as an autotransformer, i. e., the primary andsecondary coils are connected in series so that their voltages areadditive.

It has been found that there is a variety of applications where it ismost desirable that a pair of electric discharge devices be used in onecircuit and with one transformer. It will be readily apparent that suchan arrangement permits considerable saving of space and equipment wheretwo or more devices are to be used. In such arrangements, rather-thanprovide the exceedingly high voltage which would be necessary if thelamps were started simultaneously it is customary to provide circuitswhereby the lamps will be lighted in sequence. In such circuits, thetransformer is generally provided with a pair of secondary coils, one ofwhich is connected across the first lamp to be lighted and the other ofwhich is connected across the second lamp to be lighted. It has beenfound, however, that such circuits often require that a very highvoltage be impressed across the first secondary coil in order to lightthe first lamp, and that once thefirst discharge device has been ignitedthe voltage across the first secondary coil increases to an even greatervalue thereby becoming even more undesirable. Such high voltages are farin 6SS of those which would perice mit economical and compact design ofthe coils without any fear of failure thereof. Thus, it is mostdesirable to maintain the voltage drop across the secondary coils at avalue sufficient to start their associated electric discharge devices insequence but little, if any, in excess of that value. It is, of course,also necessary that the coils provide suflicient impedance to limit thecurrents to the desired value when the electric discharge devices are inoperation.

It is therefore an object of this invention to provide an improvedballast transformer which will incorporate the advantages set forthabove.

Further objects and advantages of this invention will become apparentand the invention will be better understood by reference to thefollowing description and the accompanying drawing, and the features ofnovelty which characterize this invention will be pointed out withparticul arity in the claims annexed to and forming a part of thisspecification.

This invention, in one embodiment thereof, provides a ballasttransformer for use in a starting and operating circuit for a pair ofelectric discharge devices. The transformer includes a capacitor adaptedto be connected in series with one of the devices, and is provided witha core, a primary coil adapted to be connected to a source ofalternating current, and a pair of serially connected high leakagereactance secondary coils wound on the core and adapted to be connectedacross the one destarts, one of the secondary coils is adapted to remainconnected across it for current control purposes while the othersecondary coils adapted to be connected in 'autotransformer relationwith the primary coil across the other device in order to start it.

In :a preferred modification of the invention, a third secondary coil isprovided in tightly coupled relation to the primary coil. This thirdcoil is in series relation with the other two, and its voltage issubtractive with respect to the other two. The three coils are adaptedto be connected across the one device, and the net voltage is sufiicientto cause it to start. Subsequent to starting of the one device, theoperation is the same as before.

In the drawing, I

Figure 1 is a schematic diagram of a circuit including a ballasttransformer constructed in accordance with the preferred embodiment ofthis invention;

Figure 2 is a schematic illustration of a circuit including a ballasttransformer constructed in accordance with the other embodiment of thisinvention;

Figure 3 is a voltage vector diagram after one dis-- Referring now toFigure 1, there is shown a circuit including a preferred ballasttransformer for operating a pair of electric discharge devices 1 and 2,such as fluo-v rescent lamps for instance. Lamp 1 is provided with apair of electrodes 3 and 4 and lamp 2 has a similar pair of electrodes 5and 6. While the electrodes shown in connection with the lamps 1 and 2of Figure 1 are of the cold cathode start" type, that is, no preheatingof the electrodes is provided, it will, of course, be understood thatsuch preheating may be provided if so desired.

A ballast transformer, generally indicated by the nu meral 7, has a core14, and positioned thereon is a primary coil 8 connected "across a pairof lines 9 and 10 which are adapted to lead to a source of alternatingcurrent (not shown). Transformer 7 is further provided with a secondarycoil 11 positioned on core 14 so as to be tightly coupled to primarycoil 8. The tight coupling may be effected by winding coil 11 on thesame leg as coil 8, either in the same core opening or in a differentcore opening without a leakage gap therebetween as is well known in theart. In addition, second and third secondary coils 12 and 13 are alsoWound on the core 14 of transformer 7. Each of these latter secondarycoils is provided with a loose coupling to the primary coil 8, that is,they are of the high leakage reactance variety to supply the necessaryimpedance to limit the current during operation of the lamps. The highreactance may be obtained by the use of leakage gaps, such as areindicated schematically at 15 and 16, as is well known in the art. Asshown by the instantaneous polarities indicated in Figure 1, the voltageacross coil 11 is subtractive with relation to the voltages across coils12 and 13 respectively. Lamp 1 is connected in series with a capacifor17, and through secondary coil 13, in series with lamp 2.

When it is desired to start lamp 1, there is impressed across the lamp avoltage drop determined by the voltages of coils 11, 12 and 13 incombination with, as previously stated, the voltage of coil 11 beingsubtractive. However, the net voltage is sutficient to start the lamp,and it will be observed that both secondary coils 12 and 13 are used forthe starting of lamp 1 so that an extremely high voltage across eitherone of these two secondary coils is not required.

Referring now to Figure 3, the voltage relationships after the startingof lamp 1 are set forth. It will be seen that ample voltage is providedin order to start lamp 2 and that this voltage is supplied without anunusually high voltage appearing across any one of the secondary coils.It will further be observed from Figure 3 that the presence of closelycoupled winding 11 permits a relatively small voltage across secondarycoil 12 during the subsequent starting of lamp 2.

Referring now to Figure 4, the voltage vectors of the differentcomponents of the circuit are shown when both lamps 1 and 2 are inoperation. It will be apparent that both coils 12 and 13 have voltagesacross them which are maintained well within desirable limits duringoperation, as opposed to the very high voltages frequently encounteredduring operation in the loosely coupled secondary coils of previouscircuits of this type. It will be observed that the inclusion of theadditional tightly coupled coil 11 permits the previously describedchanges in voltage through the coils 12 and 13 to be effected withoutany unnecessary or undesirable reduction in impedance because thesubtractive voltage is achieved through a tightly coupled coil which haslittle effect insofar as the reactance is concerned.

During operation, the current passes through lamp 1, capacitor 17, coil13, and lamp 2; it will be observed that the lamps are operated inseries, and that coil 13 provides the required impedance, with thecapacitor providing the power factor correction made desirable by thepresence of the impedance.

Referring now to Figure 2 of the drawmg, a second embodiment ofthis'invention will be described using like numerals for like parts. Theprincipal difference between the Figures 1 and 2 is that the tightlycoupled secondary coil 11 of Figure 1 has been omitted in the ballasttransformer shown in Figure 2. As before, loosely coupled secondarycoils 12 and 13 are so arranged that they are connected across lamp 1with their voltages being additive for starting purposes. When it isdesired to start lamp 1, the voltages of coils 1 2 and 13 will beadditive across the lamp so that the undesirablesituation of an tr m lyhi h vo tag a ss a in l 91 s elim nat as before. Referring now toFigured, which shows the voltage situation after the lighting of thefirst lamp, it

will be observed that, as with the previous circuit, ample voltage isprovided across lamp 2 in order to cause ignition thereof. Referring nowto Figure 6, it will be observed that, once both lamps have beenstarted, the voltages across coils 12 and 13 are maintained withinsatisfactory limits. The achievement of these relatively low voltagespermits, of course, a more economical construction without forfeitingthe advantages of this type of circuit.

It will be seen from the foregoing description that the two baliasttransformers set forth in the drawing each. provide a sequence startingand series operation of two electric discharge devices wherein, at allpoints of starting and during operation, the voltages across thesecondary coils are maintained within satisfactory levels so thatadequate voltage is present for the purpose to be fulfilled, and yet ahighly economical structure is available because the voltage ismaintained at a value no higher than that necessary. While specificembodiments of the invention have been set forth in the drawings and inthe above description, it will of course be apparent that improvementsand modifications may be made without departing from the scope of theinvention as defined in the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

c l. A ballast transformer for a pair of electric discharge devicescomprising a capacitor adapted to be connected in series with one ofsaid devices, a core, a primary coil wound on said core and adapted tobe connected to a source of alternating current, a pair of seriallyconnected high leakage reactance secondary coils wound on said core andadapted to be connected across said one device, said secondary coilsbeing so wound that their voltages are additive thereby to start saidone device, one of said secondary coils being adapted to be connected inautotransformer relation with said primary coil across said other deviceatfer starting of said one device thereby to start said other device.

2. A ballast transformer for a pair of electric discharge devicescomprising a capacitor adapted to be connected in series with one ofsaid devices, a core, a primary coil wound on said core and adapted tobe connected to a source alternating current, a pair of seriallyconnected high leakage reactance secondary coils wound on said core andadapted to be connected across said one device, said secondary coilsbeing so wound that their voltages are additive thereby to start saidone device, one of said secondary coils being adapted to be connected inautotransformer relation with said primary coil across said other deviceafter starting of said one device thereby to start said other device,said one secondary coil being adapted to connect in series with saiddevices during operation thereof thereby to limit current flowtherethrough.

, 3. A ballast transformer for a pair of electric discharge devicescomprising a capacitor adapted to be connected in series with one ofsaid devices, a core, a primary coil wound on said core and adapted tobe connected to a source of alternating current, three secondary coilswound on said core, two of said secondary coils being of the highleakage reactance type and being so Wound that their voltages areadditive, the third of said secondary coils being tightly coupled tosaid primary coil and being so wound that its voltage is subtractivewith relation to the first two of said secondary coils, said secondarycoils being connected in series and being adapted to be connected acrosssaid first device, said three secondary coils having anet voltage whenso connected sufl'lcientto start said first device, one of said highleakage reactance secondary coils being adapted to be connected inautotransformer relation with said primary coil across said other deviceafter starting of said one device thereby to start said other device.

-4. A ballast transformer for a pair of electric discharge devicescomprising a capacitor adapted to be connected in series with one ofsaid devices, a core, a primary coil Wound on said core and adagJted tobe connected to a source of alternating current, three secondary coilswound on said core, two of said secondary coils being of the highleakage reactance type and being so wound that their voltages areadditive, the third of said secondary coils being tightly coupled tosaid primary coil and being so wound that its voltage is subtractivewith relation to the first two of said secondary coils, said secondarycoils being connected in series and being adapted to be connected acrosssaid first device, said three secondary coils having a net voltage whenso connected sufficient to start said first device, one of said highleakage reactance secondary coils being adapted to be connected inautotransformer relation with said primary coil across said other deviceafter starting of said one device, said one high leakage reactancesecondary coil being adapted to be connected in series with said devicesand between the same during operation thereof thereby to limit currentflow therethrough.

References Cited in the file of this patent UNITED STATES PATENTS2,683,243 Feinberg July 6, 1954

